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Vegetative Morphology and Anatomy of the Salt Marsh Rush, Juncus Roemerianus Lionel N View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Aquila Digital Community Gulf Research Reports Volume 5 | Issue 2 January 1976 Vegetative Morphology and Anatomy of the Salt Marsh Rush, Juncus roemerianus Lionel N. Eleuterius Gulf Coast Research Laboratory DOI: 10.18785/grr.0502.01 Follow this and additional works at: http://aquila.usm.edu/gcr Part of the Marine Biology Commons Recommended Citation Eleuterius, L. N. 1976. Vegetative Morphology and Anatomy of the Salt Marsh Rush, Juncus roemerianus. Gulf Research Reports 5 (2): 1-10. Retrieved from http://aquila.usm.edu/gcr/vol5/iss2/1 This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf and Caribbean Research by an authorized editor of The Aquila Digital Community. For more information, please contact [email protected]. Gulf Research Reports, Vol. 5, No. 2, 1-10 VEGETATIVE MORPHOLOGY AND ANATOMY OF THE SALT MARSH RUSH, JUNCUS ROEMERIANUS LIONEL N. ELEUTERIUS Gulf Coast Research Laboratory, Ocean Springs, Mississippi 39564 ABSTRACT The extensive rhizome development found in Juncus roemerianu$ makes this species unique among rushes and is a biological feature responsible, in part, for its domination of large tracts of salt marsh. Branching in certain mature plants is distinctly sympodial, while in most it is obscured by precocious development of the continuation bud and appears to be monopodial. Each vegetative unit is composed of a scaly rhizome which grows to varying lengths and then abruptly turns up at the end to become an erect shoot. A continuation rhizome consistently arises from an axillary bud in a ventral scale leaf. Transitional leaves (large scale leaves) accompany development of the erect shoot. Rhizome scales, transitional and foliage leaves are distichously arranged and in the same vertical plane. The culm forms through an elongation of an internode of an erect shoot. Other rhizomes may also arise from buds in the axils of the transitional and foliage leaves. From one to seven terete leaves with a bifacial sheath are produced from the apical meristem of the erect stem. Fibrous roots occur laterally on erect shoots. Non-fibrous roots occur on the ventral surface to the rhizomes. The internal rhizome and root anatomy resembles that reported for most other species of Juncus while the leaf anatomy is very similar to that of Juncus maritimus and Juncus acutus. INTRODUCTION were dug out for morphological study. Plant material was taken from more than 20 different habitats. These habitats Juncus roemerianus Scheele is a rush dominating major varied in several ways: leaves of J. roemerianus in some tracts of salt marsh on the Atlantic and Gulf coasts of the places were abundant, sparse, tall, short, in pure stands and United States (Eleuterius, manuscript in preparation). The associated with other vascular plants. Plants were also ex- most successful herbaceous plants occurring in these mari- amined from low, intermediate and hypersaline marshes, as time marshes are those which are perennial and reproduce were plants colonizing new terrain, where they grew without vegetatively by vigorous rhizome growth, thus leading to the competition. Plant material for anatomical work was fmed formation of dense stands. Once established, these species in a formalin, proprionic acid and ethyl alcohol solution do not generally rely on the sexual cycle for maintenance (FPA), processed using a tertiary butyl alcohol series and of the closed stand. The importance of understanding the embedded in the usual manner. Sections were cut 10-15 structure of herbaceous species has become apparent in the microns on a rotary microtome, affiied to slides using study of crop plants where solution of practical problems Haupt's adhesive and stained with safranin and fast green arises (Hayward 1938; Bonnett 1935, 1940). Only through using standard procedures outlined by Johansen (1940) and fundamental knowledge of the pattern of growth, entailing Sass (1958). basic morphology and anatomy, can proper analysis of variation in species be attained. Structural studies of salt VEGETATIVE MORPHOLOGY marsh species have similar importance since successful man- agement of estuaries will ultimately require familiarity with General each wild species to the same extent and detail now available for cultivated crop plants. A single mature plant of J. roemerianus is difficult or Although there are several reports (Adamson 1925; Cutler impossible to discern by cursory examination in a typical 1969; Stace 1970) on the internal anatomy of various Juncus stand. Rhizomes may connect hundreds of erect shoots of a species, comparable studies on the vegetative morphology single plant in a relatively small surface area of marsh. The are lacking. Some general morphological aspects of certain continuous proliferation and subsequent senescence of rushes are described by Buchenau (1906) and Richards and rhizomes account for the vegetative spread and maintenance Clapham (1941). Anderson (1974) in a general anatomical of the mature stand (Eleuterius 1975). Long, interconnected survey of seven salt marsh plants in North Carolina also rhizomes bearing erect shoots and roots represent a portion included descriptions of some anatomical features of J. of a single clone and serve to illustrate the typical mature roemerianus. The present study describes in detail the vegeta- plant. The vegetative axes of the mature plant are dimorphic tive morphology, pattern of growth, and anatomy of mature with a clear distinction between horizontal and erect shoots plants of J. roemerianus as found in Mississippi. (Figure 1A), but the sequence of events typical of sympodial branching is often obscured by the vigorous growth asso- METHODS AND MATERIALS ciated with the horizontal axis. Plant portions consisting of rhizomes (subterranean seg- The Rhizome ments 30 to 60 cm in length) bearing erect shoots and roots Rhizomes possess tightly overlapping leaf-like scales or 2 ELEUTERIUS cataphylls which arise ventrally and dorsally. The plane of being about 2.5 centimeters (Figure 2C--E). distichy is vertical. The rhizome apex does not grow in- definitely but eventually becomes an indeterminate erect, The Erect Shoot leafy shoot. Young rhizome portions are generally larger in diameter than older parts, which become somewhat con- The mature erect shoot may vary from one to several stricted with age. Rhizomes range in diameter from 2 to centimeters in length and consists of a series of nodes and 18 mm, the average ones being about 9 mm. The internode compressed internodes. The growth of the erect shoot is length may vary from a millimeter or less to over a centi- determinate, culminating in the production of terete leaves meter. The rhizome bud is formed periodically in the axil of or a culm. Apparently as the erect shoot develops, the scale a scale leaf which arises on the lower surface of the rhizome leaves become longer and tougher in texture as each succes- (Figure 1B-E). The division of the rhizome apex is almost sive node is produced. These may be conveniently referred dichotomous with the resulting dorsal meristem being only to as transitional leaves, contrasting with the scale leaves of slightly larger than the ventral. The dorsal and ventral the rhizome and terete foliage leaves. There are generally meristems are destined to form the erect shoot and new three to five present on each erect shoot. The arrangement rhizome, respectively. In most instances the terminal rhi- of transitional and foliage leaves is distichous. zome bud develops precociously and continues to grow at A culm is apparently not produced on every erect shoot, such a rapid rate that the sympodial branching pattern is some of which then remain leafy throughout their existence. obscured to the extent that it may be erroneously inter- The culm is an elongated internode of the erect shoot, which preted as monopodial. The precocious growth of the rhi- elevates meristematic tissue destined to be the inflorescence. zome bud displaces the terminal bud of the previous unit, A red band circumscribes the floral-meristem (node) of the which becomes an erect, leafy shoot. This displacement culm and separates the internode region from the bract occurs in such a way that the leafy shoot appears to be which subtends the inflorescence. Culm production termi- inserted at the middle or, more often, toward the distal end nates the life of the erect shoot. However, the rhizome units of the rhizome internode. Occasionally, a rhizome may arise supporting the erect shoot may remain alive. The culm from a bud formed on the dorsal side of the rhizome apex appears externally much like a leaf; however, it is weakly which grows in a direction opposite the terminal rhizome developed and is broken more easily than the leaf. when eviction of the leafy shoot occurs. The apex of the dorsal rhizome becomes oriented in the opposite direction The Foliage Leaf from that arising from the ventral bud. As many as three rhizomes may arise from a single erect shoot. These new All foliage leaves are cylindrical or unifacial above the rhizomes may occur in the same or opposite directions. sheath with the abaxial surface to the exterior. The lower Most new rhizomes arise in leaf axils on the side of the portion or sheath of the foliage leaves is bifacial with free erect shoot synonymous to the ventral surface of the rhi- margins through which new leaves emerge. All sheaths are zome (Figure 1F-G). Deflection of apexes by obstructions rolled and the leaf margins form a slit through which sub- in the substratum causes many planes of growth or centri- sequent leaves protrude as they are produced by the apical fugal spread of the plant. Consequently, all new rhizome meristem of the erect shoot. The position of the slit alter- production is in one plane.
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